In homes that do not have basements or crawl spaces, one of the most dreaded things is the slab leak: a water leak under the concrete slab foundation. It can cause plenty of damage if left without repair. Fixing this plumbing problem is not as difficult as it may seem.
Identify the location of the leak. If this is a hot water leak, walking around with bare feet will probably lead you right to the area. Mark the area with masking tape.
Remove the flooring from the area. Try to remove as little flooring as possible--a square-foot piece--to prevent extensive damage and replacement.
Using a concrete drill bit, begin to drill through the concrete. Since the slab is about 4 inches thick, this will take some time. Make an opening big enough for your hand to fit in so that you can reach down to feel the leak. Once you have located the leak, make the opening bigger to repair the pipe.
Shut the water at the main and, using a pipe cutter, cut off the piece of pipe that is leaking. Replace the type of pipe you removed with an identical piece, whether copper or PVC. If PVC, cut a new piece to length and replace it the same way you would for any other PVC pipe repair. If it is copper, you will need to weld the piece into place. Leave this hole open for a day or two to make sure that the leak is properly sealed.
Mix a bag of concrete and fill the hole to the top, sealing it with the surrounding slab. Leave to dry and cure for several days.
Once the concrete is cured, use construction adhesive to secure a new piece of flooring in place.